Synthetic functional fluids



United States Patent 3,197,408 SYNTHETIC FUN CTEGNAL FLUIDS Robert A. Clipper, Ridgefield, Conn., and Carl A. Wolf,

In, New York, N.Y., assignors to Union Carbide Corporation, a corporation of New York No Drawing. Filed Dec. 16, 1%0, Ser. No. 76,162 22 Claims. (Cl. 252-515) This invention relates to lubricating oil compositions of good viscosity and anti-sludging characteristics, and more particularly, to the improvement of providing lubricating oil compositions having improved anti-corrosive action on metals.

A wide variety of ester type synthetic lubricants are known in the art as being useful as lubricants for aircraft turbine engines having high compression ratios and increased power outputs, such as turbojet and turboprop combustion engines. The use of synthetic esters has made it possible to extend the range of ambient temperatures encountered and allow increased engine operating temperatures.

However, the synthetic esters commonly employed as lubricants suffer from the disadvantage of being corrosive towards metal, particularly at high temperatures. It is immediately apparent that much damage can occur to vital parts of an engine by the use of lubricants which have corrosive action towards metal.

Accordingly, it is the object of this invention to provide lubricating oil compositions offering increased corrosion protection towards metals.

It has now been found that the anti-corrosion characteristics of synthetic esters can be markedly improved by the addition to, or the treatment of, said esters with certain nitrogen-containing heterocyclic compounds.

The nitrogen-containing heterocyclic compounds useful for the preparation of improved ester lubricants can be represented by the following formulas:

wherein X represents nitrogen or sulfur and R represents a phenyl radical or the radical N(R) wherein R represents hydrogen or an alkyl radical having from 1 to 8 carbon atoms with the proviso that at least one R must be N(R') Specific compounds encompassed by this formula include melamine, N,N,N"-triphenylmelamine and benzowherein X represents nitrogen or sulfur and Y represents hydrogen or N(R) wherein R represents hydrogen or an alkyl group having from 1 to 8 carbon atoms.

Specific compounds encompassed by this formula include benzimidazole and 2-aminobenzothiazole.

(3) Compounds containing the linkage R W R deli-1h as part of the heterocyclic ring structure. In the above formulas, W represents oxygen or sulfur, and R represents hydrogen or alkyl groups having from 1 to 8 carbon atoms. The compounds represented by (3) can be varied since the only important feature is the presence of the above-mentioned linkages. Examples of compounds represented by (3) include cyanuric acid, alloxantin, ethylene urea, ethylene thiourea, allantoin, acethylene diurene, barbituric acid and barbital.

The improved lubricants of this invention are conveniently prepared by incorporating from 0.01 to 1.0 percent and preferably 0.05 to 0.25 percent by weight of the nitrogen containing heterocyclic compounds with a synthetic base fluid or mixtures of synthetic base fluids and heating for 5 to 30 minutes at a temperature within the range of and lower to 200 C. and higher. Since most of the nitrogen-containing compounds are not entirely soluble in the base fluid to which they are added, it is desirable to filter out the undissolved material after the fluid has been treated.

The reasons why the treatment of base fluids with the described nitrogen-containing compounds is effected is not completely understood. However, the fact remains that lubricants are obtained which have superior anticorrosive properties.

The term base fluid, as used in the specification and the claims, refers to synthetic esters including diesters polyesters, and polyglycol derivatives which are used as bases for lubricants.

The synthetic base fluids to which the nitrogen-containing heterocyclic compounds are added are well known in the art. It is to be understood that the novel lubricants of this invention contain a base fluid or mixtures of base fluids which are conventional. The inst-ant invention does not reside in the particular base fluids, but rather in the treatment of conventional base fluids to obtain lubricants having superior anti-corrosive action on metals, particularly copper and lead.

The base fluids which can be treated according to the invention include:

(A) Diesters of aliphatic dicarboxylic acids which correspond to the general formula:

COOK

wherein n is an integer from 2 to 18, preferably from 2 to 12, each R represents alkyl or cycloalkyl radicals having from about 5 to 24 carbon atoms, and preferably from about 5 to 18 carbon atoms, and R represents hydrogen or alkyl groups having from 1 to 4 carbon atoms. The dicarboxylic acids may be substituted, such as, for example, B-methyl glutaric acid, to obtain lower viscosities at low temperatures so long as this substitution is consistent with the need for obtaining a low freezing point. Specific examples of organic dicarboxylic acids from which the esters may be derived are suberic, adipic, brassilic, Japanic, sebasic, glutaric, azelaic, and pimelic acids, as well as mixtures of these acids. The preferred acids are azelaic, adipic, and sebacic acids.

The alcohols used to form the diester of the acid may be branched chain or straight chain, saturated or unsaturated, aliphatic or cycloaliphatic alcohols. Typical alcohols which may be employed include Z-ethylhexyl alcohol, isooctyl alcohol, isodecyl alcohol, 2-ethylbutyl alcohol, cetyl alcohol, n-octyl alcohol, amyl alcohol, oleyl alcohol, 2-butyloctyl alcohol, methyl and dimethyl cyclohexanol, and the 0x0 alcohols, such as the mixed branched chain nonanols, prepared from the reaction of carbon monoxide and hydrogen upon olefins which normally have a branched chain structure. Mixtures of alcohols can also be used such as a mixture of 2-ethylhexyl and isodecyl alcohol.

Representative synthetic diester lubricants which can be employed in conjunction with this invention include di-(Z-ethylhexyl)sebacate, di-(2-ethylhexyl)azelate, di- [mixed-(2-ethylhexyl, isodecyl) ]azelate, (ii-(isooctyl) amlate, di-(l-methylcyclohexylmethyl)sebacate, di-(2-ethylhexyl decyl)-azelate, di-(2-ethylhexyl-2-propylheptyl) azelate, di-(2,2,4-trimethylpentyl)sebacate, di-(2-methylpentyl decyl)azelate, di-(1-ethylpropy1)adipate, di-(B-methylbutyl)adipate, di-(1,3-dirnethylbutyl)adipate, di-(Z-ethylbutyl)adipate, di-(Z-ethylhexyl) adipate, di- (isooctyl) adipate, di-(undecyl)adipate, di-(tetradecyl)adipate, di-(heptadecyl) adipate, di-(2,2,4-trimethylphenyl) adipate, di-(1 methylcyclohexylmethyl) adipate, di (l-ethylpropyl) azelate, di-(3-methylbutyl)azelate, di-(Z-ethylbutyl)azelate, di-( l-ethylpropyl)sebacate, di-(3-methylbutyl) sebacate, di-( 1,3-dimethylbutyl) sebacate, di- 2-ethylbutyl sebacate, di-(Z-ethylhexyl)sebacate, di (2-(2'-ethylbutoxy)ethyl) sebacate, di-(undecyl)sebacate, di-(tetradecyl)sebacate, di-(heptadecyDsebacate, di-(Z-ethylhexyl)glutarate, di- (undecyl) glutarate, di-(tetradecyl)glutarate, and the like.

(B) Esters of aromatic acids which correspond to the general formula:

Z(COOR wherein Z represents a phenyl radical or a naphthyl radical, n represents an integer from 2-4 and R has the same meaning as previously described.

Examples of acids from which the esters can be prepared include phthalic, terephthalic, pyromellitic, naphthalene-1,4-dicarboxylic acid, etc. The alcohols which are reacted with the aromatic acids are the same as those mentioned under (A).

(C) Complex glycol centered esters having the general formula:

wherein n represents a number from 3-51, R represents alkyl or cycloalkyl radicals having from 4 to 24 carbon atoms and R represents hydrogen, methyl or ethyl.

Examples of the above esters include 3-mehyl-1,5- pentanediol diisodecanoate and hexarnethylene 1,6-glycoldiisooctanoate.

(D) Complex glycol centered esters containing recurring ether linkages represented by the formula:

wherein R represents alkyl or cycloalkyl radicals having from 4 to 24 carbon atoms, R represents hydrogen, methyl, or ethyl and wherein n, m and X represent an integer from 1-25.

Examples of the above esters include dipropylene glycol dipelargonate, polyethylene glycol 200 di-valerate and polypropylene glycol 425 di-Z-ethyl hexanoate.

(E) Polyol monobasic acid esters corresponding to the formula:

R C[CHzO( J(CH )mCH;]u

wherein n is an integer from 3 to 4 and R represents an alkyl group having from 0-8 carbon atoms, with the proviso that when R is 0, n is 4, and m is an integer from 0 to 18.

Examples of alcohols which are reacted with aliphatic monocarboxylic acids include trimethylol ethane, trimethylol propane and pentaerithrytol.

It is to be understood that the above classes of base fluids are representative of art recognized fluids and are merely illustrative of some of the base fluids useful in this invention. The complex esters have been described in the art as well as in U.S. Patents 2,575,195; 2,575,196; and 2,703,811.

(F) Alkyl terminated polyesters-These are complex polyesters prepared from polyhydric alcohols and polybasic acids wherein reactive carboxyl or hydroxyl groups are terminated by reaction with either monofunctional alcohols or acids. These esters are known in the art and described in US. Patent 2,705,724. The disclosure of said patent is incorporated by reference into this application.

(G) Non-terminated 0r hydroxyl terminated polyesters.This class of compounds refers to those polyesters having free hydroxyl groups in the polymer chain which are blocked or terminated by reaction with monofunctional or polyfunctional compounds. These compounds are known in the art and can be prepared by reacting a dibasic acid with a glycol or alkane diol as disclosed in US. Patent 2,929,786 or by reacting a dibasic acid with mixtures of polypropylene glycol and a 1,3-alkanediol as disclosed in copending application Ser. No. 718,971, filed March 4, 1958, and now abandoned.

(H) Polyalkylene glycol derivatives.-These compounds can be represented by the formula:

wherein R represents hydrogen or an alkyl radical having from 1-12 carbon atoms, R represents hydrogen or an alkyl radical having from 1-2 carbon atoms and each of n, m and X represent a positive integer from 125.

The integers in and n can be varied so as to provide homoand heteropolymers, i.e., polyoxyethylene glycols, polyoxypropylene glycols, mixed poly(oxyethylene-oxypropylene) glycols and also the monoand diethers of the above.

This class of compounds is well-known in the art and the individual members of this class can be made in a variety of ways. Illustrative of the above class of compounds, as well as methods for the preparation of individual members are US. Patents 2,293,868; 2,425,755; 2,425,845; 2,448,664; 2,520,611 and 2,520,612.

The preferred compounds in this class are the monobutyl ethers.

It is to be understood that this invention relates to the treatment of base fluids in a novel manner and not to the particular base fluids employed. Thus, the above class of base fluids ((A) to (H)) are representative of base fluids which can be treated according to the novel process of this invention. It is also within the scope of this invention to treat mixtures of base fluids which have been designated by (A) to (H).

It is to be understood that the novel lubricants of this invention can contain conventional additives, e.g., viscosity index improvers, detergents and antioxidants, as is customary in this art. The preferred antioxidants are amine compounds such as phenothiazine, N-phenyl-beta-naphthylamine, N-phenyl-alpha-naphthylamine, and phenolic compounds such as di-tert.-bu-tyl para-cresol and butylated hydroxylanisole.

The following table depicts the critical specifications of a gas turbine lubricant and :is based upon U.S. Specification Mil-L-7808C. Somewhat similar specifications are required for turboprop lubricants as described by EMS 35E of the Allison Division of General Motors Corporation and Specification D. Eng. RD. 2487 (Second Issue) of the British Ministry of Supply.

TABLE I.-CRITICAL GAS TURBINE AIRCRAFT LUBRICANT SPECIFICATIONS Corrosion and oxidation Standard 347 352 1 F. test test Weight Change, rug/sq. cm.:

Copper i0. 4 :t=0. 4 =|:0. 2 :b0. 2 ii). 2 3:0. 2 :lzO. 2 11:1. Viscosity change, 100 F., percent 5 to 5 to +15 Ncut. No. increase, mg. KOH/g 2.0 2.0

SOD lead corrosion, 1 hr. at 325 F., rug/sq. in 6.0 (Max Corrosion, hr. at 450 F., mgJsq. in.:

Copper 3.0 (Max) Silver. 3.0 (Max) Panel eoking8 hours at 600 F 80.0 (Main) Test methods The 352 F. corrosion and oxidation test was employed as the primary tool to evaluate urea-treated fluids. The 352 F. test, designed to simulate the standard military corrosion and oxidation test (791.5308.4) was simplified by eliminating aluminum, magnesium, and silver metals, and adding a lead specimen. Steel and copper coupons are used in both tests. The 352 F. test consists of maintaining the test fluid at test temperature in the presence of the steel, copper, and lead specimens for 72 hours While purging with air at the rate of 5 liters per hour. At the completion of the test, the fluid is observed for the separation of insolubles and for viscosity change. The weight change of the metal specimens is also determined.

The SOD (Standard Oil Development Company) lead corrosion test was also used. This is the standard test procedure employed by the military for evaluating the tendency of gas turbine lubricants to corrode lead. The Allison Division (General Motors Corporation) aircraft gas turbine lubricant specifications include the SOD lead corrosion test. This test consists in rotating copper and lead (weighed) specimens for one hour in the test fluid which is maintained at 325 F. During the test, air is passed through the fluid at a rate of 57 liters per hour. The weight change of the lead specimen, in milligrams per square inch, is determined. At the present time, all lubricant specifications containing this test allow a maximum lead corrosion value of 6.0 milligrams per square inch. Values under 1.0 milligram per square inch are highly desirable.

The following tables illustrate the improved properti of the novel lubricants of thi invention.

TABLE ll-MELAMINE TREATMENT OF ALI- PHATIC DIBASIC ACID ESTERS Antioxidaut=0.5% N.F. purified phenothiazine.

352 F. corrosion and oxidation test data-Fe, Cu, and Pb metals present;

Treating condition Percent Metal condition Metal weight change, Melamine vis. mg./cm. Diester wt. change Insolubles percent F.

Temp., C. Time, min. Copper Lead Steel Copper Lead C -C azelate None +2. 2 Moderate- Dull bronze. Gray-black +0.05 Nil 0. 37 (ls-Ow azelate None d Dgllbrowndo +0. 04 0. 08 1. 6

u. C -Cio azelate 0.05 Dull orange- Dark gray- +0.03 0. 04 -2. 66

Cu. black. 0 -01 azelate LB None Dull orange- G-Btltid Nil 0. 52 8. 0

pi e 08-010 azelate 0.05 -120 15-20 Dull Dull gray +0. 04 0. 06 0. 69 0 -010 azelate None do 1111130811; +0.03 0. 12 3. 1

ac C -C1; azelate 0.05 110-120 15-20 Dull brown- G-BK +0.05 0. 03 0. 68 C -azelate 5 None Pale BK-Rmgh +0.02 -15. 9 25. 9

crus (j -azelate 5 0. 05 110-120 15-- +40. 2 Moderate- Dull brown. do +0.02 1.8 36. 4 Cg-ELZBlfitQ 5 0. 50 110-120 15-20 +28.1 d0 d0 Bright Nil 7. 1 45. 4 Di-2-ethylhexyl adipate None +2. 7 do Dill pink- Shnly3K +0. 04 Nil 2. 3

u. Dl-2-ethylhexy1 adipate" 0.05 110-120 15-20 +1.5 do Yellowdo 0. 06 +0. 06 1. 6

copper.

1 Di-(zethylhexyl, isodecyDazelate.

2 Prepared by acid catalysis and hydrogenation refining.

3 Tetra-butylorthotitaunts-catalyzed residue preparation. 4 'letra-bntylorthotitanate-catalyzed distilled preparation. 5 Di-Z-ethylhexylazelate. Prepared by acid catalysis.

G G-BK= Gray Black.

TABLE I]I.MELAMINE TREATMENT OF ALI- PHATIC DIBASIC ACID ESTERS Antioxidant=0.5% N.F. purified phenothiazine.

352 F. corrosion and oxidation test dataFe, Cu, and Pb metals present Treating condition Percent Metal condition Metal Weight change, Melamine vis. mg./cn.1. Diester w change Insolubles percent 100 F.

Temp., C Time, min. Copper Lead Steel Copper Lead (I -C azelate None +2.2 Moderate Dull bronze Gray-black. +0.05 Nil 0. 37 -010 azelate None +4. do Dlll brown- .do +0.04 0. 08 1.6

u. 03-010 azelate 0. 05 110-120 15-20 +4.4 do Drll orange- Dirk lggay- 0.03 0. 04 2. 66

u. ac 03-010 azelate None +11. 9 do Dull orange. G-B'ltI i Nil -0. 52 -8.0

pi e (l -C10 azelate 0.05 110-120 -20 +0.04 do Dull Dull gray-.. +0.04 0.06 0. 69 0 -01 azelate None +2.7 -do do Altrfilosltcz +0.03 -0. 12 3.1

ac 0 -010 azelate 0.05 -120 15-20 +2.3 do Dull brown- G-BK +0. 05 -0. 03 -0.68 Crazelate 5 None +19.9 Large Pale BK-Rtough +0.02 15.9 25.9

crus Orazelate 5 0.05 110-120 15-20 +402 Modcrate Dull brown. do +0.02 l.8 36. 4 Crazelate 0.50 110-120 15-20 +28.1 do "do Bright Nil 7. 1 45.4 Di-2-ethylhexyladipate.-- None +2.7 do D1611 pink- Sh1K +0.04 Nil -2.3

u. Di-2-ethy1l1exyladipate 0.05 110-120 15-20 +1.5 do Yellowdo 0.06 +0.00 1.6

copper.

1 Di-(2ethyll1exy1, isodecyl)azelate. 2 Prepared by acid catalysis and hydrogenation refining. 3 Tetra-butylorthotitanate-catalyzed residue preparation. 4 Tetra-butylorthotitanate-catalyzed distilled preparation. 5 Di-2-ethylhexylazelate. Prepared by acid catalysis. B G-BK= Gray Black.

TABLE 1V.-NITROGEN-CONTAINING HETERO- CYCLICS AS CORROSION INHIBITORS FOR DIESTERS 352F. corrosion and oxidation test Base fluiddi-2-ethylhexyl azelete Antioxidant0.5% (wt.) N.F. purified phenothiazine Treating conditions-l5-20 minutes at -120 0.

Metal condition Metal weight change Weight Percent mg/om. 2 Treating compound Percent vis). change Insolubles Copper Lead Steel Copper Lead None +10. 7 Large Pale Black 1rough +0.02 15.9 25.9

crus Melamine 0.05 +40.2 do Dull brown. do +0.02 1.8 36.9 Benzimidazole 2 0.10 +18.9 do Pale Bright Nil 0. 14 23.5

ms e z'aminobenzothiazolc 0.01 +19.1 do Brown do 0. 02 14.9 -13.4 2-aminobenzothiazole 0.10 +7.2 do do do +0.02 -3, 4 -14.8 Cyanurio acid 3 0 05 +328 do Pink- Bright +0.05 -0. 53 4.4

copper black spots. Oyanurio acid 010 +403 d0 Brown Bright +0.03 -0. 70 -12.0 Barbituric acid 0. 1O +23.0 d0 Dull pinkd0 +0.04 0. 18 -41.3

copper. Brabital 0.10 +28.1 Milderate- Light cop- .do Nil 22.8 -12.3

' arge. per. Allantoin 0.10 +26. 9 do Pinkd0 +0.02 -l7.8 -8. 1

copper. Alloxantin 0.10 +45.8 do .....(1 +0.03 9.5 19.9 N,N, "-Triphenylmelamine.- 0.10 +23. 0 Moderate- Light copdo Nil 14.3 5.2

per.

1 All additives insoluble in the diester unless otherwise noted. 2 Soluble in diester. 3 Very slightly soluble.

CYCLICS AS CORROSION INHIBITORS FOR DIESTERS 352 F. corrosion and oxidation test Base fluiddi-(2-ethylhexyl, isodecyDazelate Antioxidant0.5% (Wt.) N .F. purified phenot'niazirie Treating conditions1520 minutes at 115-120 C.

Metal condition Metal weight change Weight Percent mg./cm. Treating compound 1 Percent visbehlange Insolubles Copper Lead Steel Copper Lead 1. None +4.5 M0derate Dull G-BK +0. 04 0.03 -1.6

Brown- Copper. 2. Melamine 0. 05 +4.4 do Dull Dark G- +0.03 -0.04 -2.66

Orange- BK. Copper. 3. Cyanuric acid 0. 05 +3.8 Small to Dull Dull gray- Nil -0.09 0. 11

moderate. Brown- Copper.

4. Acetylene diurene 0. 05 +6.8 do Brgwu- G-BK +0.02 0.08 -1.06

opper. 5. IBenzoguanamine 0.05 +2.5 do Red-Brown. Broyvn- Nil Nil -2. 53

B ack. 6. Benzimidazoie 0.05 +3. 7 Small Dull Dull gray... Nil -0. 01 O. 10

oyanurio acid 0. 05 7. Benzimidazole- 0.05 +2.8 do Gold- Dark gray" Nil 0.05 -0. 19

Cyanurie aeid 0. 05 Copper Hydantoin 0.10 8. Benzin1idazole 0.05 +2.8 Small to do 1o Nil -0.04 0. 21

Cyanurie acid 0. 05 moderate. Hydantoin 0v 1 Additives essentially insoluble, unless otherwise noted. 2 Gray-Black. l1 Soluble.

TABLE VI.-TREATMENT OF MISCELLANEOUS COMPLEX ESTERS 352 F. corrosion and oxidation testssteel. copper and lead present Antioxidant-0.5% N.F. purified phenothiazine Treating condition Percent Metal condition Metal weight change Treating comvis. mi a/em. Complex ester pound Wt. percent E212? Insolubles Temp C. Time, min. Copper Lead Steel Copper Lead 1. Polyester None +1 19 Small Dull pale G-BK Lu- Nil -3.2 6.1 2. Polyester Melamine 0.05 110120 20 +1.3 Very smalL. Glld- G-BK Nil --0.04 3.1

opper 3. Polyester None +5.0 Small to Dull Dull gray Nil 0.07 -0.1=l

moderate. 4. Polyester Benzimidazoie, -120 20 +4.7 d0 Gold- Dull-light +0.02 +0.02 -0.08.

0.05, Cyanuric Copper gray. Acid, 0.05. 5. Polyester None +2.0 None Pale Pink. G-BK Nil -0.24 1.24 6. Polyester Benzimidazole, 110120 20 -11.7 Small Orange Light Nil Nil -0. 28

0.05, Cyanuric Copper Brown- Aeid, 0.05. O 7. Polyester Ethylene Urea, 110-120 20 1.8 V. SmalL--. Dull G-BK Nil 0. 23 0. 92

0.05. 8. Polyester Ethylenc-Thio- 110-120 20 +4.6 Moderate Dull, Pale do Nil 1.09 0. 79

urea, 0.05. Etched. '9. Polyester N -1.4 None Dull, Pale. Bright Nil --0.24 -0.04

Silverblue 10. Polyester Benzoguanamine 110-120 20 0.54 do Dull do Nil 0. 18 0.04

1 Prepared by reacting adipic acid, 3-methylpentanediol-1,5, and iso-de 2 Gray-Black.

3 1,2,6-Hexanetriol 2-ethylhexylazelate.

(triester) cylalcohol (OX0) in a 1.0:0.66:0.83 moi ratio.

4 Tested in blend containing 80% CB-C-N-AZGIEHJB, 19.5% Polypropylene glycol 425 azelate, and 0.5% Phenothiazine.

1 1 TABLE VII.CRITICAL SPECIFICATION TEST DATA ON ESTER-TYPE FLUIDS TREATED WITH MELAMINE SAMPLES CONTAINED 0.5% PURIFIED PHENOTHIAZINE Flash point.

SOD lead corrosion, mgJsq. in

Corrosion after 50 hr. at 450 F., rug/sq.

Copper 0. 2 0.3 Lead 0.5 0. 1 Corrosion-oxidation at 347 F.wt.

changes, rug/sq. cm.:

Copper nil. 0.0 Magnesiumnil nil Aluminum nil 0.0 Steel nil 0.0 Silver nil nil 100 F. viscosity change, percen +2 -3 Neut. N 0. increase, mg. KOH/g- 1.1 0.8 Panel coking, 8 hrs. at 600 F., mg. 12. 8 15. 9

* See the following table:

Weight percent C e A volate 79. 6 Melamine treated polypropylene glycol 425 Azelate- 19. 9 N. F. purified phenothlazine 0.

The following examples will illustrate the actual preparation of the novel lubricants.

EXAMPLE I Di-(Z-ethylhexyl, isodecyl) azelate was prepared as a residue product by reacting commercial grade azelaic acid with isodecyl alcohol (from the Oxo process) and an excess of 2-ethylhexanol in the presence of a catalytic amount of tetrabutyl orthotitanate, removing the water of reaction by suitable means. After a sufficiently low acid number was achieved, the reaction was stopped, the excess Z-ethylhexanol was stripped from the reaction mixture and the product filtered through a diatomaceoussilica filter bed resulting in diester A. The diester had viscosities of 3.37, 13.10, and 10,559 centistokes at 210, 100 and 65 F., respectively. A portion of this diester was treated with 0.05 percent melamine by mixing thoroughly at 110 C. for a period of minutes and filtering (Diester B). Dicsters A and B were submitted to a corrosion and oxidation test at 352 F. in the presence of metallic steel, copper, and lead. The test consisted of passing air through 100 grams of the test fluid contained in a flask equipped with a reflux condenser and thermometer. After the test, the weight change of the metals and the viscosity change of the fluid were determined. Test data are shown in the following table:

A portion of the residue diester from Example No. '1' was distilled under vacuum to produce a product having viscosities of 3.29, 12.70, and 9686 centistokes at 210, 100, and B, respectively. This diester was called Ad. A portion of the distilled product was treated with 0.05 percent melamine for 15 minutes at 110 C. followed by filtration (diester Bd). Corrosion and oxidation test data for the distilled diesters are shown in the following table:

Ester Ad+0.5% Ester Bd+0.5% (wt.) purified (wt) purified phenothiazine pheuothlazine Viscosity change, F., percent- +2. 7 +2. 3 Insolubles Moderate Moderate amount amount Metal weight change, mgJcmfl:

eel. +0.03 +0.05 Copper 0. 124 0. 03 Lead--- 3. 1 0. 68

EXAMPLE 111 A sample of distilled di [mixed (2 ethylhexyl, isodecyl)] azelate was prepared by a conventional esterification procedure, using sulfuric acid as a catalyst. The product (Ester C) had viscosities of 3.26 and 12.3 centistokes at 210 and 100 F., respectively. A portion of this diester was treated by mixing thoroughly with 0.05 percent melamine for 15 minutes at 115 C. followed by filtration (Ester D). Corrosion and oxidation test data are shown in the following table:

A sample of di-[mixed-(Z-ethylhexyl, isodecyl)] azelate was synthesized by tetrabutyl orthotitanate catalysis in the presence of 0.05 percent melamine. Except for the addition of melamine, this diester was treated the same as for Ester A. The diester (Ester E) which had viscosities of 3.37, 12.56, and 10386 at 210, 100, and -65 F., respectively, had corrosion and oxidation characteristics as shown in the following table:

Ester E+0- phenothiazine Viscosity change at 100 E, percent...

2. 9 Insolubles Moderate amount EXAMPLE V A sample of commercial di-Z-ethylhexyl adipate (Ester F) was subjected to the corrosion and oxidation test together with a sample of the same ester which was treated with 0.05 percent melamine for 10 minutes at -1l0 C. (Ester G). Treatment was melamine improved the corrosion and oxidation stability of the diester as shown by the data in the following table:

EXAMPLE VI A hydroxyl-terminated polyester was prepared by reacting a polyoxy-1,2-propylene glycol having a molecular weight of approximately 425 and azelaic acid in a 1:1.15 molar ratio. The product (code: Polyester I) had viscosities of 181 and 1838 centistokes at 210 F. and 100 F., respectively, and an acid number of 0.06. A portion of the polyester was treated by stirring at 120 C. for 15 minutes in the presence of 0.05 percent melamine followed by filtration through a bed of powdered diatomaceous silica. (This polyester is referred to as Polyester Q.) Each of these polyesters was blended with a sufficient quantity of di-[mixed-(Z-ethylhexyl, isodecyl)] azelate to meet the 7.5 centistokes at 210 F. minimum viscosity requirement for commercial turboprop aircraft lubricants. This polyester-diester blend was subjected to the corrosionoxidation test referred to above with the results which are shown in the following table:

81.5% (Wt.) diester, 18.0% (Wt.) I, 0.5% (Wt.) purified 81.5% (Wt.) diester, 18.0% (Wt.) Q, 0.5% (Wt.) purified phenothiazine phenothiazine Viscosity change at 100 F., percent.-- 1. 3 1. 4 Insolubles None Small amount Metal weight change, mg lcmfi:

Steel. Nil Nil 0. 18 -0. 3. 1 0. 82

EXAMPLE VII A complex ester was prepared by reacting adipic acid,

3-methyl-1,S-pentanediol, and isodecyl alcohol (Oxo) in a molar ratio of 1.0 to 0.66 to 0.83 in the presence of tetrabutyl ortho-titanate as the catalyst. This complex ester (Ester R) had viscosities of 15.17 and 97.18 centistokes at 210 F. and 100 F., respectively, and an acid number of 0.48. A sample of ester R was treated with 0.05 percent melamine by mixing thoroughly for minutes at 110 C. (Ester S). The data in the following table illustrate the dramatic improvement obtained by melamine treatment.

99.5% (Wt.) 99.5% (wt) Ester R Ester S 0.5% (Wt.) 0.5% (Wt.) phenothiazine phenothiazine Viscosity change at 100 F., percent... +14. 9 +1. 3 Insolublcs Small amount Small amount Nil Nil 3. 16 0. 04 6. 1 3. 1

EXAMPLE VIII is POLYOXYPROPYLENE GLYCOL UCON LUBRICANT LB-625 Weight percent composition 0.5% phenothiazine 0.05% cyanuric Acid 0.05% benzimida-zole 0.5% phenothiazine 352 F. corrosion-oxidation testmetal weight change, mg./

cmfl:

+0. 08 +0. 01 0. 20 0. 07 ea 0. 53 0. 04 SOD lead corrosion, 2

hrs. at 325 F. mg./ in. 3. 1 0. 19

EXAMPLE IX A fluid composed of 33 percent by weight of a polyoxypropylene glycol monobutyl ether having a Saybolt Universal viscosity of approximately 114-5 seconds at F. (Ucon Lubricant LB1145) and 67 percent by Weight of di-2-ethylhexy1 azelate was inhibited with 0.5 percent by weight of purified phenothiazine and tested by the 352 F. corrosion and oxidation test and the SOD lead corrosion test. Reduction in corrosivity of this blend upon the addition of small concentrations of cyanuric acid and benzimidazole is illustrated in the following table: a

UCON LUBRICANT LB-1145-DI-2-ETHYL HEXYL AZELATE BLEND Weight Percent Composition *99A7 blend *99.5% blend 0 0 phenotlnazme 0.5% phenotluazrne 005% cyanuric acid 0.05% benzirnidazole 352F. corrosion-oxidation test-metal weight change, mgJcm.

Iron Nil Nil Copper 0.55 0.07 ea -0. 04 0. 07 SOD Lead Corrosion,m gJin. 0. 73 -0. 13

* 33% (Wt.) Ucon LB-1145.

67% (Wt.) Di-2-Ethylhexyl Azelate.

EXAMPLE X A sample of commercial di(isodecyl) adipate prepared from adipic acid and isodecyl alcohol obtained by the 0x0 process was inhibited with 0.5 percent of purified phenothiazine. A second sample was prepared which contained 0.05 percent cyanuric acid, and a third sample contained 0.05 percent each of cyanuric acid and benzimidazole. The improvement obtained by the addition of the nitrogen-containing heterocyclic compounds is shown by the data in the following tablei 1 Di-isodecyl Adipate. 2 Phenothiazine.

EXAMPLE XI A lubricant formulation containing 30 percent by weight of di-isodecyl adipate, 69 percent by weight of di-isooctyl adipate, and 1 percent by weight of a polyoxypropylene glycol monobutyl ether having a S.U.S. viscosity at 100 F. of approximately 1715 (Ucon Lubricant LBl7l5) was tested for corrosiveness towards metals before and after the addition of small concentrations of benzimidazole and cyanuric acid. Phenothiazine was employed as the antioxidant in these compositions. The data in the following table illustrate the improvement in lubricant quality due to the nitrogen-containing heterocyclics.

MIXED ADIPATE DIESTER-UCON LUBRICANT LB-l715 BLEND Weight percent composition 99.5% blend 0.5% henothiazine 99.5% blend 0.05 a cyanuric acid 0.5% phenothiazine 0.05% beiizimidazo e 352 F. Corrosion-Oxidation Test-metal weight change, mgJcmfl:

Iron +0. 03 +0. 01 Copper. 0. 0. 06 ead 4. 58 -0. 16 SOD lead corrosion, mg./in. 39. 2 1. 2

See the following table:

. Percent Dl-isodecyl adipate UCON LB l715 1 Di-isooctyl adipate- .0. 69

What is claimed is:

1. A synthetic lubricant composition comprising a synthetic base fluid selected from the group consisting of ester-based fluids and polyalkylene glycol base fluids and a corrosion inhibiting amount for said synthetic base fluid of cyanuric acid as a corrosion inhibitor for said base fluid.

2. The synthetic lubricant composition of claim 1 wherein the corrosion inhibitor is a corrosion inhibiting amount of the combination of cyanuric acid and benzimidazole.

3. The composition of claim 1 wherein the synthetic base fluid corresponds to the formula:

wherein n is an integer from 2 to 18, each R is individually selected from the group consisting of alkyl and cycloalkyl radicals having from 5 to 24 carbon atoms and R is selected from the group consisting of hydrogen and alkyl groups having from 1 to 4 carbon atoms.

4. The composition of claim 1 wherein the base fluid corresponds to the formula:

Z(COOR wherein Z is a radical selected from the group consisting of a phenyl radical and a naphthyl radicals; n represents an integer from 2 to 4; and each R is individually selected from the group consisting of alkyl and cycloalkyl radicals having from 5 to 24 carbon atoms.

5. The composition of claim 1 wherein the base fluid corresponds to the formula:

wherein each R is selected from the class consisting of alkyl and cycloalkyl radicals having from 4 to 24 carbon atoms, R is selected from the class consisting of hydrogen and alkyl groups containing from 1 to 2 carbon atoms, and n is an integer from 3 to 51.

6. The composition of claim 1 wherein the base fluid corresponds to the formula:

R4 R4 R4 R4 wherein R is selected from the class consisting of alkyl and cycloalkyl radicals having from 4 to 24 carbon atoms, R is selected from the class consisting of hydrogen and alkyl groups containing from 1 to 2 carbon atoms, and n, m and X are integers from 1 to 25 7. The composition of claim 1 wherein the base fluid corresponds to the formula:

wherein R is selected from the class consisting of hydrogen and an alkyl radical having from 1 to 12 carbon atoms, R is selected from the class consisting of hydrogen and an alkyl radical having from 1 to 2 carbon atoms, and each of n, m and X are positive integers from 1 to 25.

8. The composition of claim 1 wherein the base fluid is an non-terminated polyester.

9. The composition of claim 1 wherein the base fluid is an alkyl-terminated polyester.

10. The composition of claim 1 wherein the base fluid is Z-ethylhexyl, isodecyl azelate.

11. The composition of claim 1 wherein the base fluid is di-Z-ethylhexyl adipate.

12. The composition of claim 1 wherein the base fluid is an ester of azelaic acid and a polyoxypropylene glycol having an average molecular weight of 425.

13. The composition of claim 1 wherein the base fluid is a mixture of an ester of azelaic acid and propylene glycol having an average molecular weight of 425 and Z-ethylhexyl, isodecyl azelate.

14. The composition of claim 1 wherein the base fluid is a polypropylene glycol monobutyl ether.

15. The composition of claim 1 wherein the base fluid is a mixture of a polypropylene glycol monobutyl ether and di-2-ethylhexyl azelate.

16. The composition of claim 1 wherein the base fluid is a mixture of di-(isodecyl) adipate, di-(isootcyl) adipate and a polyoxypropylene glycol monobutyl ether having a F. S.U.S. viscosity of 1715.

17. The composition of claim 1 wherein the base fluid is di(isodecyl) adipate.

18. A synthetic lubricant consisting essentially of mixed 2-ethylhexyl, isodecyl esters of azelaic acid and a corrosion inhibiting amount of cyanuric acid.

19. A synthetic lubricant consisting essentially of di(2- ethylhexyl)azelate and a corrosion inhibiting amount of cyanuric acid.

20. A synthetic lubricant consisting essentially of a polyoxypropylene glycol monobutyl ether, and a corrosion inhibiting amount of the combination of cyanuric acid and benzimidazole.

21. A synthetic lubricant consisting essentially of a polyoxypropylene glycol monobutyl ether, di-Z-ethylhexyl adipate, and a corrosion inhibiting amount of the combination of cyanuric acid and benzimidazole.

22. A synthetic lubricant consisting esssentially of a polyoxypropylene glycol monobutyl ether, di-isodecyl adipate, di-isooctyl adipate, and a corrosion inhibiting amount of the combination of cyanuric acid and benzimidazole.

References Cited by the Examiner UNITED STATES PATENTS 2,066,173 12/36' Calcottetal. 252-515 2,154,097 4/39' Loane 2s2 47.s

(Other references on following page) 1 7 UNITED STATES PATENTS 4/43 Miller et a1 44-63 2/45 Lincoln et a1. 10/49 Nunn 252-392 2/50 Moyer et a1 252-855 1l/52 Schaefier 252-392 11/52 Schaetfer 252-390 7/55 Chenicek 252-50 3/57 Patton 252-475 2/60 Lawrence et a1 252-515 3/60 Young et a1 252-56 7/60 Langer et a1 252-56 5/61 Halter et a1 252-515 6/63 LoW et a1 252-515 FOREIGN PATENTS 4/28 France.

18 OTHER REFERENCES Shock et a1., Prediction of Corrosion in Oil and Gas Wells, The Petroleum Engineer, Ref. Annual 1951, pp. B86, B88, B90, B92, B94, B96, B98 pertinent.

Cole et aL, Survey of the Literature on Antioxidants and Anticorrosion Additives for Lubricants at Elevated Temperatures, WADC Tech. Report 53-353, Wright Air Development Ctr, Wright-Patterson AFB, Ohio (1954). Recd Scientific Lib. Feb. 4, 1957, TJ 1077V5, p. 10 pertinent.

McTurk, Synthetic Lubricants, USAF Wright Air Development Center Technical Report 53-88 (October 1953), printed by McGregor & Werner Inc., Dayton, Ohio (March 1954), pp. 20-21, 33-34, 43-44 pertinent.

DANIEL E. WYMAN, Primary Examiner.

JULIUS GREENWALD, Examiner. 

1. A SYNTHETIC LUBRICANT COMPOSITION COMPRISING A SYNTHETIC BASE FLUID SELECTED FROM THE GROUP CONSISTING OF ESTER-BASED FLUIDS AND POLYALKYLENE GLYCOL BASE FLUIDS AND A CORROSION INHIBITING AMOUNT FOR SAID SYNTHETIC BASE FLUID OF CYANURIC ACID AS A CORROSION INHIBITOR FOR SAID BASE FLUID. 